Summary Activated retina-specific T cells that have acquired the ability to break through the blood-retinal barrier are thought to be causally involved in autoimmune uveitis, a major cause of human blindness. It is unclear where these autoreactive T cells first become activated, given that their cognate antigens are sequestered within the immune privileged eye. We demonstrate in a novel mouse model of spontaneous uveitis that activation of retina-specific T cells is dependent on gut commensal microbiota. Retina-specific T cell activation involved signaling through the autoreactive T cell receptor (TCR) in response to non-cognate antigen in the intestine, and was independent of the endogenous retinal autoantigen. Our findings not only have implications for etiology of human uveitis, but also raise the possibility that activation of autoreactive TCRs by commensal microbes may be a more common trigger of autoimmune diseases than is currently appreciated.

Tumor cells can co-opt the pro-migratory activity of chemokines and their cognate G protein-coupled receptors (GPCRs) to metastasize to regional lymph nodes or distant organs. Indeed, the migration toward SDF-1 (stromal cell-derived factor-1) of tumor cells bearing CXCR4 [chemokine (C-X-C motif) receptor 4] has been implicated in the lymphatic and organ-specific metastasis of various human malignancies. Here, we used chimeric G proteins and GPCRs activated solely by artificial ligands to selectively activate the signaling pathways downstream of specific G proteins, and showed that CXCR4-mediated chemotaxis and transendothelial migration of metastatic basal-like breast cancer cells required activation of members of the Gα12/13 G protein family and of the small guanosine trisphosphatase Rho. Multiple complementary experimental strategies, including synthetic biology approaches, indicated that signaling-selective inhibition of the CXCR4-Gα13-Rho axis prevents the metastatic spread of basal-like breast cancer cells.

Breast cancer metastasis is a leading cause of death by malignancy in women worldwide. Efforts are being made to further characterize the rate-limiting steps of cancer metastasis, i.e. extravasation of circulating tumor cells and colonization of secondary organs. In this study, we investigated whether angiotensin II, a major vasoactive peptide both produced locally and released in the bloodstream, may trigger activating signals that contribute to cancer cell extravasation and metastasis. We used an experimental in vivo model of cancer metastasis in which bioluminescent breast tumor cells (D3H2LN) were injected intra-cardiacally into nude mice in order to recapitulate the late and essential steps of metastatic dissemination. Real-time intravital imaging studies revealed that angiotensin II accelerates the formation of metastatic foci at secondary sites. Pre-treatment of cancer cells with the peptide increases the number of mice with metastases, as well as the number and size of metastases per mouse. In vitro, angiotensin II contributes to each sequential step of cancer metastasis by promoting cancer cell adhesion to endothelial cells, trans-endothelial migration and tumor cell migration across extracellular matrix. At the molecular level, a total of 102 genes differentially expressed following angiotensin II pre-treatment were identified by comparative DNA microarray. Angiotensin II regulates two groups of connected genes related to its precursor angiotensinogen. Among those, up-regulated MMP2/MMP9 and ICAM1 stand at the crossroad of a network of genes involved in cell adhesion, migration and invasion. Our data suggest that targeting angiotensin II production or action may represent a valuable therapeutic option to prevent metastatic progression of invasive breast tumors.